Engine cooling system

ABSTRACT

An engine cooling system decreases vehicle weight caused by employing a Rankine cycle, makes it possible to improve the performance of the Rankine cycle, and includes a coolant that circulates through a cooling pump, an evaporator, an expander, and in a condenser in this order; an engine main body in which a turbocharger is arranged in an intake passage; and a radiator through which cooling water for the engine main body circulates. A sub-radiator is installed parallel to the radiator; air that is compressed by the turbocharger is used as a heating source for the evaporator; and outlet-side cooling water of the sub-radiator is used as a cooling source for the condenser.

TECHNICAL FIELD

The present invention relates to an engine cooling system, and morespecifically relates to an engine cooling system including a Rankinecycle with an improved performance while suppressing an increase invehicle weight caused by employing the Rankine cycle.

BACKGROUND ART

Conventionally, there has been a proposal to employ a Rankine cycle in avehicle in order to recover waste heat from an engine and therebyimprove the fuel economy, as described in, for example, Japanese patentapplication Kokai publication No. 11-51582 (Patent Literature 1). Forexample, engine-main-body cooling water heated by an engine main body isused as a heating source of a Rankine cycle while intercooler coolingwater cooled by a sub-radiator is used as a cooling source, so that atemperature difference between these flows of cooling water can berecovered as a power energy in a compressor (turbine).

However, when such a Rankine cycle is employed on a vehicle, the vehicleweight is increased. This may counterbalance the effect of improving thefuel economy.

Moreover, since the temperature of the engine-main-body cooling water ismerely around 100° C., it is only possible to obtain a relatively smalltemperature difference between the flows of cooling water. Hence, it isdifficult to have the Rankine cycle exhibit a sufficient performance tofurther improve the fuel economy.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese patent application Kokai publication No.11-51582

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide an engine coolingsystem capable of suppressing an increase in vehicle weight caused byemploying a Rankine cycle and capable of improving the Rankine cycleperformance.

Means for Solving the Problem

In order to achieve the above object, an engine cooling system of thepresent invention is an engine cooling system including: a Rankine cycleconfigured such that a coolant circulates through a cooling pump, anevaporator, an expander, and a condenser in this order; an engine mainbody in which a supercharger is arranged in an intake passage; and aradiator through which cooling water for the engine main bodycirculates. The engine cooling system is characterized in that asub-radiator is installed parallel to the radiator, compressed aircompressed by the supercharger is used as a heating source for theevaporator, and outlet-side cooling water of the sub-radiator is used asa cooling source for the condenser.

Effects of the Invention

According to the engine cooling system of the present invention, theheating source used for the evaporator in the Rankine cycle iscompressed air having a higher temperature than that of conventionalengine-main-body cooling water. This makes it possible to improve theperformance of the Rankine cycle, thereby improving the fuel economy.

Moreover, since compressed air is cooled using the evaporator of theRankine cycle, this eliminates the need for an existing intercooler.Hence, it is possible to suppress an increase in vehicle weight.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a configuration diagram of an engine cooling system accordingto an embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter an embodiment of the present invention will be describedwith reference to the drawing. FIG. 1 shows an engine cooling systemaccording to the embodiment of the present invention.

This engine cooling system includes a sub-radiator 2 and a radiator 3disposed in this order from a front surface of a vehicle 1. Thesub-radiator 2 and the radiator 3 are configured to perform air-coolingby utilizing vehicle-speed wind and cooling wind of a cooling fan (notshown) when the vehicle 1 is running or idling.

In a diesel engine 4, which is a cooling target of the engine coolingsystem, air A is drawn to an intake passage 5, passes through an aircleaner not shown, and is compressed by a compressor 7 of a turbocharger6. Then, compressed air 8 thus obtained is supplied to an engine mainbody 10 via an intake manifold 9.

The compressed air 8 supplied to the engine main body 10 is mixed with afuel and burned, thereby generating a thermal energy. Then, a burned gas11 thus obtained is discharged from an exhaust manifold 12 to an exhaustpassage 13. Some of the burned gas 11 is diverted as an EGR gas 15 intoan EGR passage 14, which is located in front of the intake manifold 9and connected to the intake passage 5. To the EGR passage 14, awater-cooled EGR cooler 16 and an EGR valve 17 configured to adjust aflow amount of the EGR gas 15 are disposed in this order from theexhaust passage 13 side.

Flow amounts of engine-main-body cooling water 18 for cooling the enginemain body 10 and EGR-cooler cooling water 19 used for cooling in the EGRcooler 15 are regulated by a thermostat 20. The engine-main-body coolingwater 10 and the EGR-cooler cooling water 19 are forced to circulatebetween the radiator 3 and corresponding one of the engine main body 10and the EGR cooler 15 by the water pump 13.

On the other hand, cooling water 22 diverted from the thermostat 19during warming-up time of the engine main body 10 circulates withoutpassing through the radiator 3. Note that some of the engine-main-bodycooling water 18 normally flows as the EGR-cooler cooling water 19.

A portion of the burned gas 11 which is not diverted to the EGR passage15 is released as an exhaust gas G into the atmosphere after an exhaustgas purification device 24 including DPF, SCR, and the like purifiesharmful substances by driving the rotation of a turbine 23 of theturbocharger 6.

The engine cooling system as described above is provided with a Rankinecycle 31 configured such that a coolant 30 circulates through a coolingpump 25, an evaporator 26, an expander 28 linked to an electric powergenerator 27, and a condenser 29 in this order.

A cooling side of the condenser 29 in this Rankine cycle 31 links aninlet side of the water pump 21 to an outlet side of the sub-radiator 2.Outlet-side cooling water 32 of the sub-radiator 2 (some of theengine-main-body cooling water 18 and the EGR-cooler cooling water 19after cooling) flows into the cooling side.

Moreover, a heating side of the evaporator 26 of the Rankine cycle 31 isarranged in the intake passage 5 between the compressor 7 and the EGRpassage 14. The compressed air 8 compressed to high temperature (forexample, approximately 160° C.) by the compressor 7 flows to the heatingside.

The coolant 30 which circulates through the Rankine cycle 31 iscompressed by the cooling pump 25, and heated at a constant pressure bythe high-temperature compressed air 8 in the evaporator 26, so that thecoolant 30 is turned into an over-heated vapor at high pressure. Whilethe coolant 30 is subjected to an adiabatic expansion in the expander28, an electric power is generated by driving the rotation of theelectric power generator 27. Then, the coolant 30 is cooled at aconstant pressure by the outlet-side cooling water 32 of thesub-radiator 2 in the condenser 29, and is returned to a liquid. Theelectric power generated by the electric power generator 27 is chargedin a battery (not shown) and serves as a power source for electronicparts of the vehicle 1.

As described above, unlike a conventional case, the engine-main-bodycooling water 18 is not used as the heating source for the evaporator 26in the Rankine cycle 31, but the compressed air 8 having a highertemperature is used instead. This makes it possible to improve the powerrecovering performance of the Rankine cycle 31, thereby improving thefuel economy.

For example, the power generation by an alternator is reduced because ofan increased amount of electric power generated in the electric powergenerator 27 whose rotation is driven by the expander 28 in the Rankinecycle 31. Thus, a load to the engine main body 10 is reduced, improvingthe fuel economy.

Moreover, since the compressed air 8 is cooled using the evaporator 26of the Rankine cycle 31, this eliminates the need for an existingintercooler. Hence, it is possible to suppress an increase in vehicleweight.

Note that it is needless to say that the cooling target of the enginecooling system of the present invention is not limited to the dieselengine 4 as described above, and includes a gasoline engine, as well.

EXPLANATION OF REFERENCE NUMERALS

-   1 vehicle-   2 sub-radiator-   3 radiator-   4 diesel engine-   8 compressed air-   10 engine main body-   18 engine-main-body cooling water-   25 cooling pump-   26 evaporator-   27 electric power generator-   28 expander-   29 condenser-   30 coolant-   31 Rankine cycle-   32 outlet-side cooling water (of sub-radiator)

1. An engine cooling system comprising: a Rankine cycle configured suchthat a coolant circulates through a cooling pump, an evaporator, anexpander, and a condenser in this order; an engine main body in which asupercharger is arranged in an intake passage; a radiator through whichcooling water for the engine main body circulates; and a sub-radiatorinstalled parallel to the radiator, wherein air compressed by thesupercharger is used as a heating source for the evaporator, and whereinoutlet-side cooling water of the sub-radiator is used as a coolingsource for the condenser.
 2. The engine cooling system according toclaim 1, wherein some of outlet-side cooling water of the radiatormerges with the cooling water having passed through the condenser andreturning to the sub-radiator.
 3. The engine cooling system according toclaim 1, wherein the expander is linked to an electric power generator.4. The engine cooling system according to claim 2, wherein the expanderis linked to an electric power generator.